Transmission device of an engine, particularly for an engine with variable compression rate and/or variable displacement

ABSTRACT

transmission device, particularly for an engine with variable compression rate and/or variable displacement, includes, in a cylinder housing: a combustion piston capable of moving in a combustion cylinder of the engine and secured to a transmission member; a gear engaging with a first rack of the transmission member and providing transmission of the movement between the combustion piston and a crankshaft of the engine; a connecting rod engaging, at a first end, with the gear and, at a second end, with the crankshaft; and a control member engaging with the gear and secured to a control piston. The combustion piston and the transmission member are slidably linked with the cylinder housing in a main direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/534,988, filed Jun. 9, 2017, pending, which is a national phase entryunder 35 U.S.C. § 371 of International Patent ApplicationPCT/FR2015/053391, filed Dec. 9, 2015, designating the United States ofAmerica and published as International Patent Publication WO 2016/092211A2 on Jun. 16, 2016, which claims the benefit under Article 8 of thePatent Cooperation Treaty to French Patent Application Serial No.1462389, filed Dec. 12, 2014, the disclosure of each of which is herebyincorporated herein in its entirety by this reference.

TECHNICAL FIELD

The invention relates to a transmission device for an engine,particularly for an engine with a variable compression rate and/or avariable displacement.

BACKGROUND

Such a device is known from Patents EP1407125, FR2867515 or FR2810696.It comprises, in a cylinder housing:

-   -   a combustion piston, capable of moving in a cylinder of the        engine and secured to a transmission member;    -   a gear engaging with a first rack of the transmission member and        providing transmission of movement between the combustion piston        and a crankshaft of the engine;    -   a connecting rod engaging, at a first end, with the gear and, at        a second end, with the crankshaft.

A control member, also engaging with the gear making it possible toadjust the position of the gear in the engine, and to move the end ofthe piston stroke in the cylinder. An engine is thus obtained with acompression rate and, if necessary, a displacement which may bevariable.

The cylinder housing elements may be made of different materials so asto optimize the overall weight of the engine without compromisingperformance thereof. Thus, people often chose to use a steel crankshaft,whereas the cylinder housing is often made of aluminum. In this case,and as a result of the heating of the engine components during operationthereof, the differential expansion between the various materials of theparts, results in a movement of the mobile members of the transmissiondevice with respect to each other.

Accordingly, during the operation of the engine, the moving members ofthe transmission device are thus placed in a position of equilibrium,which may deviate from the initially desired design position. Thisposition of equilibrium, in the transmission devices known in the stateof the art, is not controlled. It results from the degrees of freedomand degrees of blocking imposed by the nature of the links between thevarious moving members composing the transmission device. This positionof equilibrium, when not controlled, may lead to excessive wear of thecomponent parts of the mobile members; or be a source of running noise.Several stable positions of equilibrium, in which the moving members canbe placed according to the nature of the disturbance they receive andwhich move the same away from their design positions, may also exist.

FIGS. 1A and 1B thus schematically show a design position and a positionof equilibrium of some mobile members of the transmission device of anengine with variable compression rate of the prior art, respectively.

The crankshaft 9 rests on the bearings of a cylinder housing 100, having3 cylinders identified as a, b, and c in FIGS. 1A and 1B. In eachcylinder, a combustion piston 2 a, 2 b, 2 c is secured to a transmissionmember 3 a, 3 b, 3 c. The connecting rods 6 a, 6 b, 6 c are respectivelylinked to the gears 5 a, 5 b, 5 c and to the crankshaft 9.

The crankshaft 9, which is made of steel, expands less than the cylinderhousing 100, which is made of aluminum. Accordingly, the crank pins ofthe crankshaft 9, which the connecting rods are associated with, are nolonger perfectly aligned with each of the cylinders a, b, and c. It canthus be seen in FIG. 1B that the mobile members associated with thecylinders a, b are placed in a position of equilibrium which deviatesfrom the design position of FIG. 1A, in which the mobile members of thesame cylinder assembly are aligned with each other and parallel to themain axis of the cylinder. The cylinder c is in the design position.

This uncontrolled position of equilibrium leads to accelerated wear ofthe mobile members, specifically at levels I and II of the connectingrod bearings and the piston skirts which are submitted to particularlyhigh friction as can be seen in FIG. 1B. And friction, in general, cansignificantly reduce the engine efficiency and/or the transmitted power.

In addition to the phenomenon of differential expansion that has justbeen described, other phenomena may cause disturbance leading toplacement of the mobile members of the transmission device in a positionof equilibrium different from the design position. This may be, forexample, wear of the members, the deformation under load thereof or thepresence of excessive running clearances.

BRIEF SUMMARY

An object of the invention is therefore to determine the nature of thelinks between some mobile members of a transmission system of an engineso as to control the operating position occupied by such members, whenthe transmission device is subjected to disturbances.

The invention specifically aims at avoiding or limiting friction thatappears at the piston skirts and/or at the rod bearings as a result ofthe differential expansion of the crankshaft and of the cylinderhousing.

In order to reach this goal, the object of the invention provides for atransmission device for an engine with variable compression rate and/orvariable displacement, comprising, in a cylinder housing:

-   -   a combustion piston, capable of moving in a combustion cylinder        of the engine and secured to a transmission member;    -   a gear engaging with a first rack of the transmission member and        providing transmission of the movement between the combustion        piston and a crankshaft of the engine;    -   a connecting rod engaging, at a first end, with the gear and, at        a second end, with the crankshaft;    -   a control member engaging with the gear and secured to a control        piston.

According to the invention, the transmission device is characterized inthat the combustion piston and the transmission member are slidablylinked with the cylinder housing in a main direction.

The formation of friction at the combustion piston skirt is thus avoidedor limited by perfectly controlling the operating position of thepiston, even in case of disturbances.

The link between the gear and the connecting rod advantageouslycomprises an annular linear link in the longitudinal direction; the linkbetween the gear and the transmission member comprises an annular linearlink in a main direction; and the link between the gear and the controlmember comprises an annular linear link in a main direction.

Thus, the gear can be positioned in alignment with the transmissionmember in a longitudinal direction of the engine; and the connecting rodcan move in a longitudinal direction and accommodate the disturbances,such as those resulting from the differential expansion of thecrankshaft. Friction and wear on the connecting rod bearings are thusavoided or reduced.

The link between the control piston and the cylinder housing preferablycomprises an annular linear link in the main direction and having acenter formed by the control piston.

The control member and the control piston make it possible to close thekinematic link between the gear and the cylinder housing, and such linkmakes it possible to improve the angular position along a main axis ofthe gear relative to the connecting rod and thus leads to a bettercontrol of friction between the gear and the connecting rod, especiallyat the connecting rod bearings.

According to a first embodiment, and to improve the control of therotational movements of the control member, the link between the controlmember and the cylinder housing comprises a straight linear link in thelongitudinal direction. And in an alternative solution of this firstembodiment, the link between the control member and the cylinder housingincludes an annular linear link in the main direction.

According to other advantageous and not restricting characteristics ofthe invention, taken alone or in combination:

-   -   the sliding link consists of:        -   an annular linear link between the combustion piston and the            combustion cylinder in the main direction and having a            center formed by the combustion piston;        -   a straight linear link defining a straight linear contact            line in the longitudinal direction and a punctual link            defining a single contact point in the longitudinal            direction between the transmission member and the cylinder            housing.    -   the straight linear link between the transmission member and the        cylinder housing is provided by a roller bearing on a plate of        the cylinder housing and on the transmission member.    -   the punctual link between the transmission member and the        cylinder housing includes a rib and a guide groove adapted to        receive the rib, with one being arranged on the roller and the        other one being arranged on the transmission member.    -   the gear has a central hole wherein a bore for the positioning        of a connecting rod eye by means of a transmission shaft and        wherein the annular linear link between the gear and the        connecting rod is obtained by:        -   a spacing between the inner surfaces of the central hole of            the gear and the side faces of the connecting rod eye            enabling the translational movement of the connecting rod on            the transmission shaft;        -   a rounded profile of the connecting rod eye bore for the            swiveling of the connecting rod in the central hole.        -   the annular linear link between the gear and the            transmission member respectively comprises a roll band of            the gear in contact with a raceway of the transmission            member, the bulging and U-shapes of which are engaged one in            the other.        -   the annular linear link between the gear and the control            member respectively comprises a roll band of the gear in            contact with a raceway of the control member, the bulging            and U-shapes of which are engaged one in the other;        -   the straight linear link between the control member and the            cylinder housing is provided by the contact between a            bearing surface of the control member and a surface of the            cylinder housing, with one being cylindrical with a            longitudinal axis, and the other one being flat.        -   According to an alternative solution, the annular linear            link between the control member and the cylinder housing is            provided by a body consisting of a spherical portion in            contact with a matching hole of the cylinder housing, with            the body having, on the side opposite the spherical portion,            a tab or a groove respectively engaging with a groove or a            tab of the control member.    -   the cylinder housing is provided with a pressing device for        compensating running clearances.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood when reading the followingdescription of a particular and not restrictive embodiment whilereferring to the appended figures among which:

FIGS. 1A and 1B schematically and, respectively, show the designposition and a position of equilibrium of some mobile members of anengine of the prior art.

FIG. 2 shows a principle sectional view of an engine with variablecompression rate.

FIGS. 3A and 3B show perspective and exploded views of some elements ofthe transmission device according to a specific exemplary implementationof the invention.

FIG. 3C shows a side view of some elements of the transmission deviceaccording to a particular exemplary implementation of the invention.

FIG. 3D shows a section along the axis F of FIG. 3c of some elements ofthe transmission device according to a particular exemplaryimplementation of the invention.

FIGS. 4 and 5 show perspective and exploded views of the gear in aparticular exemplary implementation of the invention.

FIG. 6 shows a perspective view of the connecting rod in a particularexemplary implementation of the invention.

FIGS. 7A and 7B show cross-sections of the control member and thecontrol piston according to two particular exemplary implementations ofthe invention.

FIG. 8 schematically shows a position of equilibrium of some mobileelements of an engine according to the invention.

DETAILED DESCRIPTION

In the following description and while referring to the figures, thefollowing definitions will be used, by convention:

-   -   the longitudinal direction is the direction defined by the major        axis of the crankshaft 9;    -   the main direction is the direction defined by the major axis of        the combustion cylinder 2;    -   the transverse direction is the direction defined by the        direction perpendicular to the previous two directions.

In addition, in the present application, “disturbances” will mean thephenomena tending to place the mobile members, when the engine isrunning, in a position of equilibrium different from the designposition. It may be, for example, and not exhaustively, wear or themanufacturing tolerance of the members leading to dimensions whichdeviate from their exact design dimensions, or movements related to thedifferentiated expansion between such members, to the deformation underload thereof or to the presence of excessive running clearances.

In FIG. 2, which shows a principle section view of an engine withvariable compression rate and/or variable displacement, a cylinderhousing 100 includes at least one combustion cylinder 110 wherein acombustion piston 2 moves in a guided translation causing the rotationof a crankshaft 9 through a transmission device 1.

The transmission device 1 comprises a transmission member 3 secured tothe combustion piston 2 and first engaging with a first connectingdevice 4 supported by a wall of the cylinder housing 100 and, on theother hand, with a first side of a gear 5.

The transmission member 3 is provided, on one of its faces, with a largerack, the teeth of which are engaged with those of the gear 5.

The gear 5 is connected, via a transmission shaft 62, to a first end ofa connecting rod 6. The second end of the connecting rod 6 is connectedto a crankshaft 9, so as to execute the transmission of the movement.

The gear 5 engages on a second side, opposite the transmission member 3,with a rack of a control member 7 capable of moving in the maindirection in engagement with a second connecting device 4′.

The control member 7 is controlled by a control device comprising acylinder consisting of a control piston 12 guided in a control cylinder112 of the cylinder housing 100. The control device ensures thetranslational movement of the control member 7 in the main direction.

In operation, the translational movement of the combustion piston 2 andof the transmission member 3 integral therewith, is initiated andmaintained by the combustion of the mixture in the combustion cylinder110. Such movement is guided by the existing link between the combustionpiston 2 and the combustion cylinder 110, and the linking device 4. Themovement is transmitted to the assembly formed by the gear 5 and theconnecting rod 6 to move the crankshaft 9 in rotation. The position ofthe control member 7 is adjusted in the main direction by the controldevice. The movement thereof is guided by the second connecting device4′ in this direction. The movement of the controller 7 causes thepivoting of the gear 5, which results in moving the end of the stroke ofthe combustion piston 2 in the combustion cylinder 110. The enginecompression rate and/or capacity thus varies.

According to the invention, the nature of the links between some mobilemembers that have just been listed is so determined as to control theoperating position occupied by such members, when the transmissiondevice 1 is subjected to disturbances.

“Controlling the operating position” means that the degrees of freedomand the degrees of blocking defining the nature of the links facilitatea movement of the parts of the mobile members relative to their ideallocations of design toward a position, which does not lead to excessiveoperating friction. Within the scope of this application, a degree offreedom or such movement will be considered as “locked” to the extentthat this degree of freedom or this movement cannot exceed the requiredminimum clearance. For example, in order to stop a translationalmovement between two components having a mutually different degree offunctional freedom, a maximum clearance of 0.04 mm to 0.2 mm is allowedin the direction of translation to be locked.

It should be noted that such an analysis is not easy, since not onlyshould each link be studied, but also the interactions between eachlink, too, for each one of the degrees of freedom and/or of blocking inorder to determine the most favorable combination. It should also benoted that the multiple blocking of some degrees may lead to thedevelopment of constraints in parts, thus, promoting wear thereof, andthat, on the contrary, excessive (relative to the expected functionalityof each member) degrees of freedom can lead to the malfunction of thedevice when it is subjected to disturbances, as has been stated in theintroduction of this application.

The prototypes and thorough studies conducted by the inventors of thisapplication have thus shown that some main links of the transmissiondevice 1, which has just been described should be precisely determined,among which:

-   -   the link between the assembly formed by the combustion piston 2        and the transmission member 3, and the cylinder housing 100.    -   the link between the gear 5 and the connecting rod 6.    -   the link between the gear 5 and the transmission member 3.    -   the link between the gear 5 and the control member 7.

The exact nature of each of these links is disclosed in detail in thefollowing paragraphs of the present description.

For example, links A between the assembly may be formed by thecombustion piston 2 and the transmission member 3, and the cylinderhousing 100.

According to the invention, the assembly of the combustion piston 2 andthe transmission member 3 is slidably linked A with the cylinder housing100 in a main direction.

As is known per se, the sliding link provides five degrees of blockingand allows a single translational movement.

According to the invention, any movement of the transmission member 3other than a translation in a main direction should thus be locked. Inother words, the linking device 4 is so configured as to block anymovement of the transmission member 3 other than a translation in a maindirection. This more particularly relates to the blocking of a swivelingmovement in the cylinder 110 of the transmission member 3 and thecombustion piston 2, which would induce friction on the inner walls ofthis cylinder.

In order to minimize friction between the parts of the link, suchsliding link A is preferably broken down into:

-   -   an annular linear link A1 between the combustion piston 2 and        the combustion cylinder 110, the center of which is formed by        the piston 2 in the main direction.    -   a straight linear link A21 in the longitudinal direction is        combined with a punctual link A22 in the longitudinal direction        between the transmission member 3 and the cylinder housing 100.

The annular linear link A1 opposes the two translations in thelongitudinal and transverse directions of the combustion piston 2, withall the other movements being free. This ensures minimum frictionbetween the contact surfaces of the combustion piston 2 with that of thecombustion cylinder 110.

The straight linear link A21 opposes the translation of the transmissionmember 3 in the transverse direction and the rotation thereof along themain axis of the combustion cylinder 110.

Eventually, the punctual link A22 provides the fifth degree of blockingof the sliding link that opposes the translation of the transmissionmember 3 in the longitudinal direction.

This ensures that the translational movement in the main direction ofthe assembly formed by the combustion piston 2 and the transmissionmember 3 relative to the cylinder housing 100 only remains free.Friction at the skirt of the combustion piston and the cylinder is thusprevented, or limited. The other five possible degrees of freedom ofsuch member are blocked, thus avoiding any strain to the parts thatmight cause situations that could cause excessive friction and/or noiseoperation, or the wear thereof.

Link C Between the Gear 5 and the Transmission Member 3

It should be reminded that the gear 5 engages with a large rack formedon the transmission member 3. In this respect, the link C between thegear 5 and the transmission member 3 comprises a first rack and pinionlink.

This rack and pinion link can be defined as a straight linear link,wherein the gear toothing is represented by a line substantiallyparallel to the axis of the gear passing through the pitch circle of thetoothing and the rack toothing is represented by a plane oriented alongthe pressure angle of the teeth, commonly 20°. This link has:

-   -   two degrees of freedom in translation in the plane which defines        same,    -   two degrees of freedom in rotation, one for the axis defined by        the direction of the line, with the other one being defined by        the normal to the plane characterizing the link.

According to the invention, the link C between the gear 5 and thetransmission device 3 further includes an annular linear link in themain direction.

This combination of links results in the blocking of the relativetranslational movement in the longitudinal and transverse directionsbetween the gear 5 and the transmission member 3, and in allowing therotational movements along the longitudinal and main axes of the gear 5relative to the transmission member 3 and the translation movement alongthe main axis.

According to the invention, the gear 5 has to be maintained centered onthe large rack of the transmission member 3, without thereby inducingsignificant constraints on the gear 5 or on the control member 7. Thegear 5 and/or the transmission member 3 are so configured as to bemaintained centered relative to one another.

It should be noted that, in the solutions known from the art, thesliding longitudinal movement of the gear 5 on the transmission member 3was possible. For this purpose, the width of the teeth of the gear 5 wasso reduced as to enable this sliding movement.

According to the present invention, the blocking of this translationalmovement by the link C makes it possible to optimize the width of theteeth of the gear 5 and thus to maximize the load that can betransmitted by the transmission device 1. The engine performances arethus improved for unchanged overall dimensions of the components (bestengine torque and higher rating).

Link D Between the Gear 5 and the Control Member 7

The transmission device 1 (FIG. 3A) also comprises a control device 7for adjusting the end of the piston stroke in the combustion cylinder110.

The link D between the gear 5 and the control member 7 includes anannular linear link in the main direction. The control member 7 isprovided with a large rack engaging with the gear 5, and the link alsoincludes a rack and pinion link.

The location of this link is thus perfectly similar to the link C seenabove. And, the gear 5 and/or the control member 7 are accordingly soconfigured as to be maintained centered with respect to one another,too.

This combination of links, therefore, leads to block the relativetranslational movements in the longitudinal and transverse directionsbetween the gear 5 and the control member 7 and enable the rotationalmovements along the longitudinal and main axes of the gear 5 relative tothe transmission member 7 and the translational movement along the mainaxis.

The issue is thus to prevent constraints from applying to the gear 5 andleading to moving same from the plane in which the previous links holdsame.

The combination of links A, C and D makes it possible to position thetransmission member 3, the gear 5 and the control member 7 in alignmentand in a position determined relative to the cylinder housing 100.

Link B Between the Gear 5 and the Connecting Rod 6

According to the invention, the link B between the gear 5 and theconnecting rod 6 comprises an annular linear link in the longitudinaldirection.

As seen previously, an annular linear link opposes two translationalmovements. In this case, the issue is opposing the translation in themain and cross directions of the connecting rod 6 relative to the gear5. All the other movements are free.

The rotation of the connecting rod 6 relative to the gear 5 is requiredto transform the translational movement in the main direction of theaxis of the gear 5 into a rotational movement of the crankshaft 9 alongthe longitudinal axis.

The translation of a connecting rod eye 61 in a longitudinal directionrelative to the gear 5 makes it possible to hold the connecting rod 6parallel to the axis of the combustion cylinder 110 even when a rod head64 is moved, as a result of the differential expansion of the crankshaft9 relative to the cylinder housing 100. The position of equilibrium ofthe connecting rod 6 in the transmission device 1 also makes it possibleto prevent or limit wear of the connecting rod bearings, and ensures amaximum power transmission.

The link B enables free rotational movements between the connecting rod6 and the gear 5 about the longitudinal axis, the transverse axis andabout the main axis. These last two rotations (about the transverse axisand about the main axis) make up for the perpendicularity defects thatmay exist, for example, between the combustion cylinder 110 and thecrankshaft 9, and in this case also, reduce friction which occurs in thetransmission device 1.

Generally, the annular linear link B between the gear 5 and theconnecting rod 6 makes it possible to dissociate the positioning, in afirst plane, of the “high” mobile members of the transmission device 1(the combustion piston 2, the transmission member 3, the gear 5 and thecontrol member 7), from the positioning in a second plane different,from the first one, and substantially parallel thereto, of the “low”mobile member of the device (the connecting rod 6, the crankshaft 9).

The combination of links A, B, C and D, which have just been listed,lead to promote when the engine is running and is independent of thedisturbances that it is subjected to, as well as the alignment of thegear 5 with the transmission member 3 and the control member 7. The linkbetween the gear 5 and the connecting rod 6 is free enough, as seenabove, to prevent the gear 5 from being driven by the movement of thecrankshaft 9 along the longitudinal axis.

In other words, the mobile members of the transmission device 1, whichhave just been described, are all positioned along the longitudinal axisin relation to the walls of the cylinder housing 100 and not, as was thecase in the described solutions of the prior art, relative to theposition of the crankshaft 9, through the connecting rod.

Link E Between the Control Member 7 and the Cylinder Housing 100

The link E between the control member 7 and the cylinder housing 100comprises, in the lower part thereof, a straight linear link E1 in thelongitudinal direction. The connecting element 4′ is so configured as toprovide this link.

This link has two degrees of blocking which enable it on the one hand tomaintain the control member 7 against the cylinder housing 100 and, onthe other hand, to prevent the rotation of this member about its mainaxis, i.e., in the main direction defined above.

This link also makes it possible to keep free the translational movementrequired to operate the engine in the main direction of the transmissionmember 7.

To absorb the geometrical defects, which may exist between the mobilemembers in the transverse direction, the link E1 can be supported by arunning clearance compensating system, as described, for example, inEP1740810, EP1979591 or in the application FR14/59791 dated Mar. 10,2014.

As seen above, the control member 7 is secured to a control piston 12guided in the control cylinder 112. The link E also comprises a link E2between the control piston 12 and the control cylinder 112 having anannular linear nature and having a center formed by the control piston12 in the main direction.

However, for a given rate adjustment, i.e., when the position of thecontrol piston 12 is fixed in the control cylinder 112, this link E2 hasa degree of freedom in translation in the main direction blocked, whichreduces it to a simple ball joint.

In this configuration, the rotational movement of the control member 7relative to the cylinder housing 100, about an axis of rotation passingthrough its apex and in the transverse direction, is preserved. Thismovement makes it possible to absorb the disturbances that develop inthe transmission device during the operation thereof, which could reduceits mechanical efficiency.

The combination of the links E1 and E2, in combination with the links A,C and D which have just been disclosed, ensures a sliding link betweenthe assembly formed by the control member 7 and the control piston 12and the cylinder housing 100.

The Link E′ Between the Control Member 7 and the Cylinder Housing 100

According to a variant of the preferred embodiment for implementing theinvention, the link E′ between the control member 7 and the cylinderhousing 100 comprises, in its lower part, an annular linear link E′l inthe main direction. The linking element 4 is so configured, in thisembodiment, as to provide such a link.

This link has two degrees of blocking which enable same, on the onehand, to maintain the control member 7 against the cylinder housing 100and, on the other hand, to prevent the translation of the lower part ofthe control member 7 in a longitudinal direction.

This link also makes it possible to maintain free the translationalmovement required to operate the engine in the main direction of thecontrol member 7, as well as the rotation of the control member 7 aboutthe main axis.

Similarly to the variant E, the link E′l can be supported by a runningclearance compensating system.

The link E′ also comprises a link E′2 between the control piston 12 andthe control cylinder 112 having an annular linear nature and a centerformed by the control piston 12 in the main direction.

However, and similarly to the variant E, for a given rate adjustment,this link E′2 has a degree of freedom in translation in the maindirection blocked, which reduces it to a simple ball joint.

In this configuration, the rotational movement of the control member 7relative to the cylinder housing 100, about an axis of rotation passingthrough its apex in the main direction, is preserved. This movementmakes it possible to absorb the disturbances that could reduce itsmechanical efficiency.

The combination of the links E′l, E′2, in combination with the links A,C and D, which have just been disclosed, ensures a sliding link betweenthe assembly formed by the control member 7 and the control piston 12and the cylinder housing 100.

Exemplary Implementation of the Invention.

FIGS. 3A, 3B, 3C and 3D show a particular exemplary implementation ofthe transmission device 1, according to the invention.

The combustion piston 2 is provided with a guide skirt 23. When, as isthe case, the guide skirt 23 has a low height relative to the diameterof the combustion cylinder 110 (FIG. 2), the link between the combustionpiston 2 and the combustion cylinder 110 forms the annular linear linkA1 between same.

The combustion piston 2 can be made of a thick disc provided withgrooves receiving the top compression rings, the compression rings, andthe scraper rings, as is well known per se.

The quality of this link can be improved by giving the guide skirt 23 aslightly bulging shape thereby limiting the intensity of friction, whichoccurs at the contact surfaces.

The link between the transmission member 3 and a wall of the cylinderhousing 100 (FIG. 2) is provided by the connecting device 4. The latterprovides, in a preferred embodiment, for the straight linear link A21and the punctual link A22.

The connecting device 4 includes a roller 40 consisting of a cylindricalbody and whereon the respective surfaces 48, 38 of a plate 41 aresupported, secured to the cylinder housing 100 and to the transmissionmember 3. The roller 40 provides for a straight linear link A21 in thelongitudinal direction. In order to synchronize the movement of thecombustion piston 2 and of the roller 40, the latter may be providedwith gears 44 at each of its ends, engaging with racks 46 associatedwith the plate 41, on the vertical edges thereof. The first and/or thesecond pinion 44 of the roller 40 may also engage with a rack 37 of thetransmission member 3. The punctual link A22 may be formed by providinga cylindrical body 42 of the roller 40 with a guide rib 43. This guiderib 43 may be placed in the middle of the cylindrical body between thepinions 44. The guide rib 43 is so designed as to be accommodated, onthe one hand, in a first vertical groove 49 formed on the plate 41, andin a second vertical groove 31 formed on the surface 38 of thetransmission member 3.

In an alternative embodiment, it can be provided so that the guide rib43 of the roller 40 will be replaced by a groove, and that the grooves49, 31 will be replaced by two guide ribs.

The gear 5, shown in greater detail in FIGS. 4 and 5, may consist of twohalf gears RI and R2 assembled in one piece. They have a central hole 53into which a bore 50 for positioning the connecting rod 61 (FIG. 3D) bymeans of a transmission shaft 62 (FIG. 3D) opening.

The annular linear link B between the gear 5 and the connecting rod 6(FIG. 2) is provided by a spacing between the inner surfaces of thecentral hole 53 and the side faces of the connecting rod eye 61 enablingthe translational movement of the connecting rod 6 on the transmissionaxis 62.

It is also provided by giving a rounded profile to the bore 63 of theconnecting rod eye 61, which receives the transmission axis 62. Thisprofile enables the swiveling of the connecting rod 6 along the main andtransverse rotation axes. The connecting rod 6 is shown in FIG. 6.

The gear 51 comprises a first toothing engaging with the teeth 34 of thelarge rack 35 of the transmission member 3. It comprises a secondtoothing 52 engaging with the large rack 73 of the control member 7.This arrangement between the gear 5, and respectively, the controlmember 7 and the transmission member 3 forms the rack and pinion linksdisclosed above.

According to the invention, such arrangement is also provided with anannular linear link C, D making it possible to keep the gear 5 centeredon the large racks 35, 73. This additional link was not present in theknown solutions of the prior art. Each toothing 51, 52 is provided, inthe middle thereof, with a groove 54 coaxial with the pitch circle ofthe gear 5. Inside each groove 54, a roll band 55 with a bulging profileis fixed. It may, for example, be a toroidal-shaped roll band. Thetransmission member 3 and the control member 7 each have a raceway 30,70, respectively, the U-shape of which matches that of the bulgingportion of the roll band 55, designed to contact and receive thisbulging part, as can be seen in FIG. 3D.

In an alternative solution, the raceways 30, 70 of the transmissionmember 3 and the control member 7 may be bulging and the roll band 55 ofthe gear 5 have the matching U-shape.

In FIGS. 4 and 5, the pivoting axis of the gear 5 located in the bore 50is positioned at the center of the pitch circle of the gear 5. Thisconfiguration makes it possible to control the engine compression rateonly via the control member 7. It is, however, possible, while remainingwithin the scope of the invention, to shift the pivoting axis of thecenter of the pitch circle of the gear 5 so as to vary the kinematics ofthe combustion piston 2 and thereby obtain a control of the enginedisplacement.

As shown in FIGS. 7A and 7B, the control element 7 is secured to thecontrol piston 12. The part of the control piston 12 in contact with theinner surfaces of the control cylinder 112, which can have a bulgingprofile, forms the annular linear link E2.

In these figures, the cylinder housing 100 is also provided with apressing device 90 making it possible to compensate for the runningclearances, which may exist between the mobile members of the engine.Within the scope of the present invention, it will be assumed that thepressing device 90 is an integral part of the cylinder housing 100.

The control member 7 is connected with the pressing device 90 of thecylinder housing 100.

FIG. 7A, corresponding to the preferred solution of implementation ofthis link, shows an exemplary embodiment of the straight linear link E1in the longitudinal direction. In this figure, the control member 7 hasa cylindrical support surface along a longitudinal axis in contact witha flat surface of a piston of the pressing device 90. In an alternativesolution not shown, the cylindrical surface along the longitudinal axiscan be supported by the piston of the pressing device 90 and come intocontact with a flat surface formed on the control member 7.

FIG. 7B shows an exemplary embodiment of the annular linear link E1′corresponding to the variant of the preferred solution of implementationof this link. A body 91 consisting of a spherical portion engages with amatching hole of the pressing device 90 in order to provide a balljoint, mobile in rotation along the three main, transverse andlongitudinal axes. The control member 7, on its face opposite the largetoothing, has a groove in which a tab of the body 91 can slide, on theside opposite the spherical portion thereof. This blocks the translationalong the longitudinal axis, with the translation along the transverseaxis being, of course, blocked by the control member 7 contacting thecylinder housing 100 of the pressing device 90. Of course, placing thegroove on the body 91 and the tab on the control member 7, could bepreferred.

FIG. 8 schematically shows a position of equilibrium of some mobilemembers of the transmission device 1 (FIG. 3A), which has just beendescribed as an example. It can be noted, contrary to the position takenby the elements shown in FIG. 1B in the case of an engine of the priorart, that, for each engine cylinder-assembly:

-   -   the combustion pistons 2 a, 2 b and 2 c and the transmission        members 3 a, 3 b and 3 c are oriented in a main direction, thus,        limiting friction with the combustion cylinders 110;    -   the gears 5 a, 5 b and 5 c are centered on the transmission        members 3 a, 3 b, 3 c;    -   the connecting rods 6 a, 6 b and 6 c are also oriented in a main        direction, thus providing an efficient transmission of forces        and limiting wear on the connecting rod bearings.

It can be seen in FIG. 8 that the members shown of the transmissiondevice 1 keep an orientation determined relative to the cylinder housing100 in spite of the disturbances caused by the displacements between thetop mobile members and the low mobile members related to the expansionin this specific example.

Of course, the invention is not limited to the examples described andvariants can be applied to the embodiments thereof, without departingfrom the scope of the invention as defined in the claims.

What is claimed is:
 1. A transmission device for an engine with avariable compression rate and/or a variable displacement, thetransmission device comprising, in a cylinder housing: a combustionpiston capable of moving in a combustion cylinder of the engine andsecured to a transmission member; a gear linked with a first rack of thetransmission member and providing transmission of the movement betweenthe combustion piston and a crankshaft of the engine; a connecting rodlinked, at a first end, with the gear and linked, at a second end, withthe crankshaft, a major axis of the crankshaft defining a longitudinaldirection; and a control member linked with the gear and secured to acontrol piston; and wherein the combustion piston and the transmissionmember are slidably linked with the cylinder housing in a maindirection, the main direction defined by an axis of the combustioncylinder, the sliding link providing five degrees of blocking andallowing a single translation movement in the main direction; whereinthe sliding link is provided by a roller bearing on a plate of thecylinder housing and on the transmission member and is provided by a riband a guide groove adapted to receive the rib, with one being arrangedon the roller and the other one being arranged on the transmissionmember; wherein a link between the gear and the connecting rod is anannular linear link in the longitudinal direction; wherein a linkbetween the gear and the transmission member is formed of a rack andpinion link and an annular linear link in the main direction; wherein alink between the gear and the control member is formed of a rack andpinion link and an annular linear link in the main direction.
 2. Thetransmission device according to claim 1, wherein the gear has a centralhole wherein a bore opens for the positioning of a connecting rod eye bymeans of a transmission shaft and wherein the annular linear linkbetween the gear and the connecting rod is obtained by: a spacingbetween the inner surfaces of the central hole of the gear and the sidefaces of the connecting rod for the translational movement of theconnecting rod on the transmission shaft; and a rounded profile of theconnecting rod eye bore for the swiveling of the connecting rod in thecentral hole.
 3. The transmission device according to claim 2, whereinthe annular linear link between the gear and the transmission memberrespectively comprises a roll band of the gear in contact with a racewayof the transmission member, the bulging and U-shapes of which areengaged one in the other.
 4. The transmission device according to claim3, wherein the annular linear link between the gear and the controlmember respectively comprises a roll band of the gear in contact with araceway of the control member, the bulging and U-shapes of which areengaged one in the other.
 5. The transmission device according to claim4, wherein a link between the control piston and the cylinder housingincludes an annular linear link in the main direction and having acenter formed by the control piston.
 6. The transmission deviceaccording to claim 5, wherein a link between the control member and thecylinder housing comprises a straight linear link in the longitudinaldirection.
 7. The transmission device according to claim 6, wherein thestraight linear link between the control member and the cylinder housingis provided by the contact between a bearing surface of the controlmember and a surface of the cylinder housing, with one being cylindricalwith a longitudinal axis, and the other one being flat.
 8. Thetransmission device according to claim 6, wherein the link between thecontrol member and the cylinder housing also comprises an annular linearlink in the main direction.
 9. The transmission device according toclaim 8, wherein the annular linear link between the control member andthe cylinder housing is provided by a body consisting of a sphericalportion in contact with a matching hole of the cylinder housing, withthe body having, on the side opposite the spherical portion, a tab or agroove respectively engaging with a groove or a tab of the controlmember.
 10. The transmission device according to claim 9, wherein thecylinder housing is provided with a pressing device for compensatingrunning clearances.
 11. The transmission device according to claim 1,wherein the annular linear link between the gear and the transmissionmember respectively comprises a roll band of the gear in contact with araceway of the transmission member, the bulging and U-shapes of whichare engaged one in the other.
 12. The transmission device according toclaim 1, wherein the annular linear link between the gear and thecontrol member respectively comprises a roll band of the gear in contactwith a raceway of the control member, the bulging and U-shapes of whichare engaged one in the other.
 13. The transmission device according toclaim 1, wherein a link between the control piston and the cylinderhousing includes an annular linear link in the main direction and havinga center formed by the control piston.
 14. The transmission deviceaccording to claim 1, wherein the cylinder housing is provided with apressing device for compensating running clearances.